It is anticipated that 50% of the speech services provided by public telecommunications networks by the year 2000 will involve mobile subscriber terminals. To provide service to these mobile subscribers, it will be necessary to locate significant numbers of roaming subscriber terminals. Serving the roaming subscribers over a plurality of different networks within large geographical areas will under current subscriber directory schemes require huge data bases and transmission/switching capacity.
Existing public land mobile networks use a centralized home location register to store subscriber information. This register is interrogated to retrieve location information. It requires a large transmission and switching capacity and requires considerable time to locate information.
Directory systems with a hierarchal tree structure for application to large scale telecommunications networks have been proposed [RACE project 1043 (mobile)]. This directory arrangement guides a cell from a home node to a visited node. However, it requires that location information be stored in all the nodes in each level of the tree including the visited and home nodes.